Noise reducer

ABSTRACT

A noise reducer is provided that ameliorates electromagnetic noise interference. More specifically, the noise reducer ameliorates electromagnetic noise interference for electronic equipment caused by noise superimposed on a conductor wire. The conductor wire includes a magnetic cylindrical core that penetrates a hollow hole, a winding coiled around the magnetic cylindrical core, and an impedance element connected to the winding. When a noise current is superimposed on the conductor wire that has been made to penetrate the magnetic cylindrical core, part of the noise current is electromagnetically induced from the conductor wire to the winding and flows to the winding. The noise current that flows to the winding is transformed into heat and consumed by the impedance element. As a result, the noise power that gives electromagnetic noise interference to the electronic devices can be reduced and the electromagnetic noise interference for the electronic devices ameliorated.

TECHNICAL FIELD

The present invention relates to a noise reducer which decreaseselectromagnetic interference caused due to noise (hereinafter, referredto as “electromagnetic noise interference”) that affects medicalequipment, computer-controlled electronic precision devices, and thelike.

BACKGROUND ART

Recently, malfunctions of medical equipment, computer-controlledelectronic precision devices, and the like as well as unintentionalsudden accelerations and the like by drives of electric automobiles andhybrid automobiles have been considered as problems. Those problems areconsidered to be based on the existence of electromagnetic noises in theenvironment where the medical equipment, computer-controlled electronicprecision devices, and the like are placed or in the environment whereelectric automobiles and hybrid automobiles are travelling.

In the meantime, noise failure is not necessarily generated in theplaces where the medical equipment, computer-controlled electronicprecision devices, and the like are placed, even though there is a largeelectromagnetic field of the electromagnetic noise. It is because thereis such state where noise failure is not generated in the medicalequipment, computer-controlled electronic precision devices, and thelike, even though there is a large electromagnetic field of theelectromagnetic noise by an inverter power supply and the like that areactually closely placed under the environment where the medicalequipment, computer-controlled electronic precision devices, and thelike are placed. Therefore, it is considered that the noise failure isgenerated due to multiple factors such as the frequency and the size ofthe noise current flown in wiring conductors in the periphery of theelectronic device, a wiring configuration of the medical equipment,computer-controlled electronic precision devices, and the like.

Currently, the problems of the noise failure generated due to theelectromagnetic waves are the important interference issue to be dealtwith for the medical equipment, computer-controlled electronic precisiondevices, and the like. Thus, various types of noise countermeasureproducts are developed and put on the market. However, the selection andmethod of use various types of noise countermeasure products andgeneration of the noise failure reduction effects thereof actuallydepend on the technical discretion of those in charge of the technologyin the manufactures of the medical equipment, computer-controlledelectronic precision devices that use the noise countermeasure products.

Next, modes of the electromagnetic noise current will be described.

The modes of the electromagnetic noise current inducing noise failureare generally classified into a normal mode (or a differential modecurrent) and a common mode current (or an unbalanced current). Aphenomenon where the common mode noise current and the normal mode noisecurrent are both superimposed on a formal signal current of a signaltransmission conductor wire connected to an electronic device is wellknown.

Therefore, the currently-used filters are structured to deal with thenoise current of both the normal and common modes. In general, theelectromagnetic noise interference in the medical equipment and thecomputer-controlled electronic precision devices is considered to begenerated mainly via a power supply line and an earth lines connected toa power lines, so that power-supply line noise filters are put on themarket and used frequently. Further, while there is no normal mode noisecurrent with a single-line earth line, it is not allowed to insert, intoa line, a noise countermeasure product that obstructs the safe functionthat is the original function of the earth line for use. Thus, thecountermeasure product thereof is limited in terms of its function.

In the meantime, the basic form of the power-supply line noise filterscurrently on the market is in the structure shown in FIG. 10. For aferrite toroidal core 20 used for an inductor coil used in a broadbandcharacteristic ferrite material that exhibits a large magneticpermeability value in the high-frequency region and an excellentlow-loss characteristic. However, even though the ferrite material is amagnetic material that exhibits the excellent broadband characteristic,it is easily magnetic-saturated even with a small current value whenused as an inductor. Thus, two coils 21, 22 are coiled around a singleferrite toroidal core 20 in many of the power-supply line noise filterson the market (e.g., Japanese Unexamined Patent Publication Hei6-233521). They are coiled to mutually cancel magnetic flux φ within theferrite toroidal core 20 as shown in FIG. 11 so that the ferritetoroidal core 20 does not lose the inductor function by beingmagnetically saturated with the normal mode power supply current ofseveral to several tens of amperes flown in the power supply line. Thus,the two coils 21, 22 exhibit no inductor function for the normal-modenoise current and have no obstructing function thereof. However, for thecommon-mode noise current considered as a minute current that is sosmall that induces no magnetic saturation in the ferrite toroidal core20 even when superimposed on the power supply line, the coils 21, 22both function as the inductor since the directions of the magnetic fluxφ become the same directions. That is, the two coils 21, 22 coiledaround the ferrite toroidal core 20 are coils that are subjected tofunction to obstruct the common-mode noise current, and those aredesigned not to be magnetically saturated by the power supply current.In general, the coiled numbers of the coils 21, 22 are designed to bethe same, and actually designed to obstruct the magnetic saturationregardless of the extent of the normal-mode power supply current value.

Patent Document 1: Japanese Unexamined Patent Publication Hei 6-233521

As described above, the inductor coil of the noise filter used for theconductor wire of the power supply line, for example, only has afunction of preventing the common-mode noise current from flowing intothe electronic device side but has no function of preventing thenormal-mode noise current from flowing in. In the currently-usedpower-supply line noise filter of the basic structure shown in FIG. 10,the function of preventing the noise current of both of the normal andcommon modes from flowing into the electronic device side is designed tocreate a short-circuit state mainly by a capacitor C so that the noisefrequency current does not flow into the electronic device side.

Next, a well-known and wide-spread noise countermeasure product using aferrite material shown in FIG. 12 will be described. Noisecountermeasure products of this type are put on the market from manyferrite material manufactures (TDK Corporation, NEC TOKIN Corporation,and the like). The noise countermeasure product is considered to exhibita noise current reduction effect by inserting a conductor wire into aninsertion hole 23 a of a cylindrical ferrite core 23. Further, the noisecountermeasure product shown in FIG. 13 is a developed type of thecylindrical ferrite noise countermeasure product shown in FIG. 12, andit is used by providing a plurality of insertion holes 24 a in aplate-type ferrite core 24 in parallel and inserting a plurality ofconductor wires thereto.

Regarding the noise countermeasure products using the ferrite shown inFIG. 12 and FIG. 13, it is assumed that the ferrite materials are soblended and sintering-processed that the loss of the magnetic substanceis small in a low-frequency region that is a frequency region of anormal signal current flown in the conductor wire and that the loss ofthe magnetic substance is large in a high-frequency noise region thatexceeds a signal frequency region. However, it is considered anextremely difficult task to adjust the noise current obstructionfrequency region by blending the materials and executing a sinteringwork.

Further, a small current value is assumed as the signal current of thenoise countermeasure products. Thus, those are employed for only theconductor wires that are not necessary to take the magnetic saturationof the ferrite material due to the current of the inserted conductorwire into consideration.

An object of the present invention is to provide a noise reducer whichreduces the noise failure generated in the medical equipment and thecomputer-controlled electronic precision devices through consuming apart of the noise current superimposed on the conductor wires such asthe power supply line and the earth line with the resistance provided ona winding-side circuit and suppressing the noise current superimposed onthe conductor wires by electromagnetic induction between the conductorwires and the windings.

SUMMARY OF THE INVENTION

That is, as shown in FIGS. 1A and 1B, the noise reducer according to thepresent invention is characterized to: use a ferrite material thatexhibits a small loss even in a high-frequency region for a cylindricalcore 2; to coil a winding 3 penetrated through a hollow part of thecylindrical core 2; and to provide an impedance element 4 to the winding3. It is designed to consume the noise current superimposed on aconductor wire 1 by the impedance element 4 by inducing it to thewinding 3 by the electromagnetic induction effect for the winding 3 andto reduce the nose interference by inserting the conductor wire 1 insidethe hollow part 2 a of the cylindrical core 2 to which the winding isprovided. As the cylindrical core used in the noise reducer according tothe present invention, a cylindrical shape may be formed bysuperimposing a plurality of existing broadband-characteristic toroidalcores or a sintering-processed core formed in a cylindrical shape in thefirst place may be used as well. It is also possible to use othermagnetic materials instead of the ferrite material.

The present invention makes it possible to reduce the noise failure byinserting the conductor wire such as the earth line or the power-supplyline into the cylindrical core of the noise reducer, and to contributeto purify the electromagnetic environment by suppressing reemission ofthe noise power to minimum.

Further, even when the conductor wire is a single earth line or two orthree lines of power supply lines, each of the individual conductorwires can be inserted and used individually. Thus, it can be utilizedeffectively for reducing the electromagnetic wave noise failuregenerated in the earth line and the multiple power-supply lines.

Furthermore, it becomes unnecessary to perform a wiring connection workof the conductor wires by simply inserting and placing the conductorwires into the cylindrical core, so that there is also an advantage ofbeing able to take a noise failure countermeasure while maintaining thecurrent wiring relation.

While the impedance element connected to the wiring is illustrated witha pure resistance in FIGS. 1A and 1B, the impedance element may be suchtype having a frequency response characteristic including a capacitorand an inductor. However, in order to clarify the explanation of thenoise electromagnetic wave environment purifying function of the presentinvention, the explanation will be provided in the embodiment of thepresent invention in the followings by referring to the case of usingonly the pure resistance shown in FIGS. 1A and 1B.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view showing a noise reducer according to anembodiment of the present invention, and FIG. 1B shows a sectional viewof a cylindrical core used in the noise reducer according to theembodiment of the present invention;

FIG. 2A is a circuit diagram for describing the state when reducing thenoise failure by inserting the conductor wire into the noise reduceraccording to the present invention, and FIG. 2B is a block diagram usedfor an explanation by enlarging the noise reducer part of FIG. 2A, whichis shown in a duplicated manner with FIG. 1B;

FIG. 3 is an equivalent circuit diagram showing a noise reducingfunction of the noise reducer according to the embodiment of the presentinvention;

FIG. 4A shows explanation charts showing a method for enhancing theelectromagnetic noise interference reduction effect by using a pluralityof the noise reducers according to the embodiment of the presentinvention, in which FIG. 4A is a case where a plurality of the noisereducers according to the present invention are inserted through asingle line such as an earth line, for example, and FIG. 4B is a casewhere those are employed for double-line type conductor wires such asconventional power-supply lines, for example;

FIG. 5 is a circuit diagram showing an embodiment of a power-supply linenoise filter in which the noise reducer according to the presentinvention and a capacitor are used in combination;

FIG. 6 is a characteristic chart showing the magnetic permeabilityfrequency characteristic of a magnetic core material;

FIG. 7 is a characteristic chart showing the magnetic permeabilityfrequency characteristic of a magnetic core material;

FIG. 8 is a perspective view showing the noise reducer according to theembodiment of the present invention, which uses cores with air gaps foradjusting inductance of the inductor and the saturated current value ofthe cylindrical cores with the air gaps;

FIG. 9 is a chart showing changes of the inductance value with respectto the changes of the angle θ between two air gaps when positions of theair gaps of the neighboring cores shown in FIG. 8 are shifted to thecircumferential direction;

FIG. 10 is an illustration showing a circuit block diagram of awidely-used power-supply line noise filter;

FIG. 11 is an explanatory illustration showing an inductor innermagnetic field of the widely-used power-supply line noise filter;

FIG. 12 is a perspective view showing a widely-used bead-type ferritenoise countermeasure product on the market; and

FIG. 13 is a perspective view showing a widely-used bead-type ferritenoise countermeasure product on the market in which the bead type isformed as a multiple-line type.

BEST MODES FOR CARRYING OUT THE INVENTION

A harness (conductor wire) for connecting between computer-controlledelectronic devices is mounted inside an engine room of an automobile,for example, and the entire length of the harness may often reachten-something meters. An ignition noise electromagnetic wave is a highfrequency of several tens of kilohertz to several megahertz, and theconductor wire of the harness is considered to work as a linearreception antenna. That is, it is a well-known fact in the field of theantenna engineering that any kinds of conductor wires all work as linearantennas, and the harness (conductive wire) is not an exception.

Therefore, the ignition noise electromagnetic wave intruded inside theengine room including a road face reflection and the like can be afactor for generating a common-mode noise current to the conductor wireof the harness, since the conductor wire of the harness works as thelinear reception antenna.

Based on that, it is considered that the noise current generated on theconductor wire of the harness induces the electromagnetic noiseinterference in the electronic control circuit and to cause a problem ofsudden speed increase unintended by the driver, etc.

The present invention is the invention designed in view of theabove-described conditions, which contributes to reducing the noisefailure accidents achieved by the theoretical investigations of thetechnical countermeasure for the electromagnetic noise.

As shown in FIGS. 1A and 1B, the basic structure of the noise reduceraccording to the embodiment of the present invention includes: acylindrical magnetic core (referred to as a cylindrical corehereinafter) 2 into which a conductor wire 1 such as a power line or anearth line where a noise is superimposed is penetrated through a hollowhole 2 a; a winding 3 coiled around the cylindrical core 2 via thehollow hole 2 a of the cylindrical core 2; and an impedance element 4connected to the winding 3. In this case, the conductor wire 1 and thewinding 3 are electrically insulated. While the impedance element 4connected to the winding 3 constituting a secondary-side winding circuitP is illustrated with a pure resistance 4 in FIGS. 1A and 1B, theimpedance element 4 may be such type having a frequency responsivecharacteristic including a capacitor and an inductor other than theresistance. However, in order to clarify the explanation of the noiseelectromagnetic wave environment purifying function of the presentinvention, the explanation will be provided in the embodiments of thepresent invention in the followings by referring to the case of usingonly the pure resistance shown in FIGS. 1A and 1B.

Specifically, as shown in FIGS. 1A and 1B, in the embodiment, thecylindrical core 2 is formed by stacking a plurality of magnetic ringcores (e.g., ferrite toroidal cores) 2 ₁, 2 ₂, - - - , 2 _(n) having theso-called broadband characteristic whose magnetic loss is small over theranges from the low frequency to the high frequency.

When there is a magnetic saturation phenomenon generated in thecylindrical core 2, the winding 3 does not function as the inductor.Thus, the noise current obstruction effect and the noise powerconsumption effect by the resistance 4 cannot be expected. Therefore,employed is a form with which the conductor wire 1 such as the powerline is simply inserted into the hollow hole 2 a of the cylindrical core2 and used in order to suppress the magnetic saturation of thecylindrical core 2 to minimum, so that the magnetic flux generatedwithin the cylindrical core 2 by the signal line current such as thepower supply current becomes minimum to deal with the magneticsaturation of the cylindrical core 2 as in the case of the ferrite beadshown in FIG. 12. The current noise countermeasure product of FIG. 12currently put on the market is also in a form which is used by insertingthe conductor wire. However, even though the ferrite core is formed toexhibit a large magnetic loss in the high-frequency region, the noisesuppression effect in the noise frequency region of less than MHz issmall.

In the meantime, the embodiment shown in FIG. 1 and FIG. 2 according tothe present invention presents the form in which the cylindrical core 2is formed by superimposing eight toroidal cores (magnetic ring cores) 2₁, 2 ₂, - - - , 2 _(n) having the broadband low-loss characteristic. Inthis case, the inductance value for the conductor wire 1 to be insertedbecomes small when the number of the toroidal cores 2 ₁, 2 ₂, - - - , 2_(n) to be superimposed is small, while it becomes large when the numberis large. Thus, the noise current suppression value and the effectivelow-limit frequency can be controlled by changing the number of thetoroidal cores 2 ₁, 2 ₂, - - - , 2 _(n) that form the cylindrical core2, the value of the resistance 4, and the coiled number N of the winding3. It is to be noted that the number of the toroidal cores (magneticring cores) 2 ₁, 2 ₂, - - - , 2 _(n) is not limited only to “8”. Whilethe ferrite toroidal cores are used as the plurality of (magnetic ringcores) 2 ₁, 2 ₂, - - - , 2 _(n), it is also possible to use othermagnetic ring cores such as silicon steel, iron, and permaloy.

While the cylindrical core is created in the form where a plurality offerrite toroidal cores are superimposed in the embodiments shown in FIG.1A and FIG. 1B, it is also possible to use a unified-typesintering-processed cylindrical core or a cylindrical core formed bycombining half-divided shapes of such type.

Further, as shown in FIG. 1B, the winding 3 of the secondary-sidewinding circuit P of FIG. 1A is coiled N-times through the hollow hole 2a of the cylindrical core 2, and the resistance 4 is connected betweenterminals 3 a and 3 b thereof. Further, the winding 3 is coiled aroundthe cylindrical core 2 in such a manner that there is no electriccontact made with the inserted conductor wire 1. It is also possible touse an inductor and a capacitor in the winding circuit P in addition tothe resistance 4 to give a frequency characteristic to the noise powerof heat consumption. In that case, the elements which thermally consumethe noise current that is electromagnetically induced by the winding 3by being connected to the winding 3 of the winding circuit P includingthe winding circuit using only the resistance 4 and the circuit usingthe resistance, the inductor, and the capacitor are referred to as theimpedance element 4. Regarding the basic structure of the presentinvention, details of the relation between inductance L₀ given to theconductor wire 1 by the cylindrical core 2 and inductance L₁ dependingon the coiled number N of the winding 3 as well as the noise failurereduction function will be described later.

With the above-described structure, the noise reducer according to theembodiment of the present invention is configured in such a manner that,when the noise current is superimposed on the conductor wire 1 such asthe power line or the earth line penetrated through the hollow hole 2 aof the cylindrical core 2, a part of the noise current iselectromagnetically induced to the winding 3 from the conductor wire 1to flow into the winding 3 and thermally consumed in the resistance 4that is provided to the winding 3, the noise power flown to the medicalequipment and computer-controlled electronic precision devices in whichthe electromagnetic noise interference is generated is reduced, and theelectromagnetic noise interference is eliminated.

As described above, even in a case where the conductor wire 1 isinserted into the hollow hole 2 a of the cylindrical core 2 to be usedin the noise reducer according to the present invention, the number ofused magnetic ring cores for forming the cylindrical core 2, the coilednumber of the winding 3, and the resistance value of the resistance 4 onthe winding 3 side may be determined as appropriate according to thestate of the noise failure and the electromagnetic environment where theelectronic device exposed to the interference is placed.

Next, the noise failure reduction function of the noise reduceraccording to the present invention will be described by using a circuitstructure model shown in FIG. 2A.

In FIG. 2A, a noise current I₀ flown by superimposing on the signalcurrent of the conductor wire 1 such as the power-supply line is acommon-mode current flown as a result when the conductor wire 1functions as a linear antenna, and the reception voltage of the linearantenna is shown as a noise voltage source E. Further, while the noisecurrent I₀ shows the form of the normal-mode current in FIG. 2A, thecommon-mode noise current can also be described by the same circuitmodel by assuming an equivalent noise load resistance R_(L) to bedescribed later. That is, regardless whether the noise current is thecommon-mode or the normal-mode, it is considered to necessarily consumethe noise power when the noise failure is generated in the medicalequipment and the computer-controlled precision device and considered tobe able to define R_(L) as an equivalent noise load resistance providedthat the power consumption amount is I₀ ²R_(L). Therefore, even in thecase of the common-mode noise current, the noise failure may simply bedealt by the model shown in FIG. 2A by considering that it is thecurrent by the interposition of a stray capacitance formed between thecasing of the device and the ground.

As described above, the embodiment of the present invention creates thenoise failure reduction effect for the device by thermally consuming apart of the noise current I₀ superimposed on the conductor wire 1 in theresistance 4 by inducing it to the winding 3 with an electromagneticinduction effect and by reducing the consumption noise power I₀ ²R_(L)in the equivalent noise load resistance R_(L).

The inventors of the present invention measured the relation between theinductance L₀ given by the conductor wire 1 inserted into the hollowhole 2 a of the cylindrical core 2 and the inductance L₁ given by thewinding 3 by L, C, R meters and have found that there is a followingrelation (1) with respect to the coiled number N of the winding 3provided that the inductance given by the conductor wire 1 inserted intothe hollow hole 2 a of the cylindrical core 2 is L₀ and the inductancegiven by the winding 3 is L₁.L ₁ ≈N ² L ₀  (1)

Next, the effect of reducing the noise current I₀ will be discussedbased on the relation of (1) described above.

In FIG. 2A, the noise power P_(RL) consumed in the equivalent noise loadresistance R_(L) are acquired. The noise power P_(RL) is the power thatgives a noise failure to the electronic device according to the noisecurrent I₀. In other words, it is the power consumed for the noisefailure. The noise power P_(RL) is acquired in a form of Expression (8)from Expressions (4) and (5) solved by simultaneous differentialequations shown in Expressions (2) and (3) assuming that the noisesource voltage is e=Ee^(jωt), the noise current I₀ is i₀=I₀e^(jωt), andthe noise current flown by being electromagnetically induced to thewiring 3 is a sine wave of i₁=I₁e^(jωt). Note here that I₀ is the noisecurrent superimposed in the conductor wire 1, and I₁ is the noisecurrent flown by electromagnetically induced to the winding 3. L₀ is theinductance given by the conductor wire 1 inserted to the cylindricalcore 2 as described above, L₁ is the inductance given by the winding 3,R_(L) is the resistance value of the equivalent noise load, and R₁ isthe resistance value of the resistance 4 connected to the winding 3.

The solutions of simultaneous differential equations of Expression (2)and (3) are shown in Expressions (4) and (5).

$\begin{matrix}{{{L_{0}\frac{\mathbb{d}i_{0}}{\mathbb{d}t}} + {R_{L}i_{0}} + {M\frac{\mathbb{d}i_{1}}{\mathbb{d}t}}} = e} & (2) \\{{{L_{1}\frac{\mathbb{d}i_{1}}{\mathbb{d}t}} + {R_{1}i_{1}} + {M\frac{\mathbb{d}i_{0}}{\mathbb{d}t}}} = 0} & (3) \\{{{\left( {R_{L} + {j\;\omega\; L_{0}}} \right)I_{0}} + {j\;\omega\;{MI}_{1}}} = E} & (4) \\{{{\left( {R_{1} + {j\;\omega\; L_{1}}} \right)I_{1}} + {j\;\omega\;{MI}_{0}}} = 0} & (5)\end{matrix}$

Assuming that M=√{square root over (L₀L₁)} (where M≧0 in this case),Expressions (8) and (9) can be acquired from the relation of L₁≈N²L₀ inExpression (1) and Expressions (6) and (7).

$\begin{matrix}{I_{0} = {\frac{R_{1} + {j\;\omega\; L_{1}}}{{R_{1}R_{L}} + {j\;{\omega\left( {{R_{1}L_{0}} + {R_{L}L_{1}}} \right)}}}E}} & (6) \\{I_{1} = {\frac{{- j}\;\omega\;\sqrt{L_{0}L_{1}}}{{R_{1}R_{L}} + {j\;{\omega\left( {{R_{1}L_{0}} + {R_{L}L_{1}}} \right)}}}E}} & (7) \\{P_{RL} = {{{I_{0}}^{2}R_{L}} = {\frac{1 + {N^{4}\left( \frac{\;{\omega\; L_{0}}}{R_{1}} \right)}^{2}}{1 + {\left( \frac{\;{\omega\; L_{0}}}{R_{1}} \right)^{2}\left( {N^{2} + \frac{R_{1}}{R_{L}}} \right)^{2}}}\frac{E^{2}}{R_{L}}}}} & (8) \\{P_{R\; 1} = {{{I_{1}}^{2}R_{1}} = {\frac{{N^{4}\left( \frac{\;{\omega\; L_{0}}}{R_{1}} \right)}^{2}\left( \frac{R_{1}}{R_{L}} \right)}{1 + {\left( \frac{\;{\omega\; L_{0}}}{R_{1}} \right)^{2}\left( {N^{2} + \frac{R_{1}}{R_{L}}} \right)^{2}}}\frac{E^{2}}{R_{L}}}}} & (9)\end{matrix}$

P_(RL) is the noise power consumed in the equivalent noise loadresistance R_(L), and P_(R1) is the noise power consumed in theresistance 4 of the winding 3. In Expressions (8) and (9), a) is anangular frequency of the noise voltage and current.

The noise power consumed in the equivalent noise load resistance R_(L)when the noise reducer according to the embodiment of the presentinvention is not used is E²/R_(L).

In the meantime, when the noise reducer according to the embodiment ofthe present invention is used, a part of the noise power is reradiatedand a part of the noise current I₀ is thermally consumed in theresistance 4 of the winding 3 by being electromagnetically induced tothe winding 3. When Expression (10) is substituted in Expression (8), ashown in Expression (10) evidently becomes smaller than 1, so that it isshown that it becomes smaller than E²/R_(L) of the noise power consumedin the equivalent noise load resistance R_(L) when the noise reduceraccording to the embodiment of the present invention is not used,thereby exhibiting the function of reducing the noise failure. Further,it is shown that a part of the noise power is consumed as the powerP_(R1) shown in Expression (9) by the resistance 4 on the winding 3side.

$\begin{matrix}{\alpha = \frac{1 + {N^{4}\left( \frac{\;{\omega\; L_{0}}}{R_{1}} \right)}^{2}}{1 + {\left( \frac{\;{\omega\; L_{0}}}{R_{1}} \right)^{2}\left( {N^{2} + \frac{R_{1}}{R_{L}}} \right)^{2}}}} & (10)\end{matrix}$

As described above, by using the noise reducer according to the presentinvention, the noise failure elimination effect can be expected byreducing the power P_(RL) consumed for generating the noise failure bythe equivalent noise load resistance R_(L).

Further, when Expression (11) is substituted in Expression (9) whichshows the noise power P_(R1) consumed in the resistance 4 of the winding3 of the noise reducer, various kinds of α and β can be acquired byselecting the values of N and R₁ of Expressions (10) and (11).

$\begin{matrix}{\beta = \frac{{N^{4}\left( \frac{R_{1}}{R_{L}} \right)}\left( \frac{\;{\omega\; L_{0}}}{R_{1}} \right)^{2}}{1 + {\left( \frac{\;{\omega\; L_{0}}}{R_{1}} \right)^{2}\left( {N^{2} + \frac{R_{1}}{R_{L}}} \right)^{2}}}} & (11)\end{matrix}$

Therefore, it becomes possible to perform a noise failure eliminationwork while reducing the environmental electromagnetic noise in the noisecountermeasure site. Thus, numerical value examples regarding the valuesof α and β when performing such work will be discussed.

The actually measured value 64 μH acquired by an impedance meter is usedfor L₀ of Expression (1) of the cylindrical core 2 shown in FIG. 1.Regarding the values of α and β by Expression (10) and (11) using thisvalue, the value of a becomes α=−3.2 dB at the noise frequency of 100KHz. α=−9 dB at the noise frequency of 500 KHz, α=−10 dB at the noisefrequency of 2 MHz. and also α=−10 dB at the noise frequency of 10 MHzor more. provided that the coiled number of the winding 3 is N=3, theresistance value of the resistance 4 is R₁=1 kΩ, the resistance value ofthe equivalent noise load resistance is R_(L)=50Ω. Further, regarding β,the value of β becomes β=0.12 at the noise frequency of 100 kHz, β=0.21at the noise frequency of 500 kHz, and also β=0.21 at the noisefrequency of 1 MHz or more.

That is, regarding the noise frequency power E²/R_(L) in this case at500 kHz or more, it is shown that 21% thereof is thermally consumed inthe resistance 4, the interference power in the equivalent noise loadresistance R_(L) is lightened to 10 to 12%, and the remaining noisefrequency power becomes the reflection power.

In the meantime, when the resistance value R₁ of the resistance 4 of thewinding 3 is changed to 5 KΩ under the same condition of L₀=64 μH, N=3,and R_(L)=50Ω, the value of α becomes α=−2.3 dB at the noise frequencyof 100 KHz, α=−12 dB at the noise frequency of 500 KHz, and α=−20 dB atthe noise frequency of 2 MHz or more. Thus, the consumption noise powerof the equivalent noise load resistance R_(L) becomes reduced at thenoise frequency of 500 KHz or more compared to the case of R₁=1 kΩ, andthe noise failure reduction effect is improved.

In the meantime, the value of β becomes β=0.03 at the noise frequency of100 kHz, β=0.07 at the noise frequency of 500 kHz, and β=0.08 at thenoise frequency of 2 MHz or more. Thus, the thermally consumed power inthe resistance 4 of the winding 3 is reduced greatly. Therefore, thereflection power is also increased greatly, so that the effectcontributing to ease the electromagnetic environment regarding the noiseelectromagnetic wave is decreased.

As described above, various kinds of α and β can be acquired byselecting the coiled number N of the winding 3 and the resistance valueR₁ of the resistance 4 under such condition from the relation shown inExpression (1) described above regarding the inductance L₀ given by theconductor wire 1 inserted to the cylindrical core 2, the inductance L₁given by the winding 3, and the coiled number N of the winding 3.Through selecting the values of α and β as appropriate, it is possibleto purify the electromagnetic environment and to reduce the noisefailure.

It is not considered to have a large environmental noise electromagneticfield under the current legal noise restriction such as CE marking.Thus, it is assumed that the equivalent noise load resistance R_(L) issmall when the noise current I₀ flown in the conductor wire 1 is large,and that the equivalent noise load resistance R_(L) is large when thenoise current I₀ flown in the conductor wire 1 is small. Therefore, inthis embodiment, it is estimated that the equivalent noise loadresistance R_(L) is about 50Ω at the most.

Further, when the resistance value of the equivalent noise loadresistance R_(L) is changed while the coiled number N of the winding 3is fixed as shown in Expressions (8) to (11), the value of theresistance value R₁ of the resistance 4 connected to the winding 3 maybe changed as appropriate to deal with the noise failure or the optimumR_(L) value for overcoming the noise failure may be selected by changingthe coiled number N of the winding 3. That is, with the electronicdevice under the electromagnetic noise interference, it is possible toselect the optimum values of N and R₁ with which the noise failure canbe reduced/eliminated and with which the electromagnetic environment atthe site of placing the electronic device can be improved. Note,however, that the value of R_(L) is considered as an intrinsic value ofthe electronic device that is under the noise failure, which is not avalue acquired by a measurement work and is a value estimated from anoise frequency current measurement value of the conductor wire 1acquired by a clamp-type oscilloscope ammeter and an electromagneticfield measurement value of an environmental electromagnetic noise.

It is needless to say that it is also possible to deal with theelectromagnetic noise interference by using a variable resistor and bymaking the value thereof variable instead of using the resistance 4 inthe noise reducer according to the present invention.

Next, the noise reduction effect and the noise electromagneticenvironment purifying function according to the present invention willbe described by referring to FIG. 3.

FIG. 3 is an equivalent circuit diagram corresponding to a transformerin which the conductor wire 1 penetrating through the hollow hole 2 a ofthe cylindrical core 2 formed by stacking the magnetic ring cores 2 ₁, 2₂, - - - , 2 _(n) is a primary winding and windings 3 ₁, 3 ₂, - - - , 3_(n) coiled around the cylindrical core 2 by being inserted into thehollow hole 2 a of the cylindrical core 2 are secondary windings.

While there is one winding 3 shown as the secondary winding and thecircuit element of the winding circuit P constituted with that winding 3is shown as the pure resistance 4 in FIGS. 2A and 2B, it is alsopossible employ the structure shown in FIG. 3. That is, as shown in FIG.3, there may be a plurality of windings 3 ₁, 3 ₂, - - - , 3 _(n) coiledindividually and separately around the cylindrical core 2. Further, itis also possible to set a plurality of individually separated windingcircuits P₁, P₂, - - - , P_(n) formed by the plurality of windings 3 ₁,3 ₂, - - - , 3 _(n). Furthermore, as the impedance element 4 connectedto the windings 3 ₁, 3 ₂, - - - , 3 _(n) of the plurality of secondarywindings, not only a type constituted with a single pure resistance butalso an impedance element 4 including a resistance as well as aninductor and a capacitor may be used as well.

Therefore, in FIG. 3, the impedance elements 4 are shown with Z₁ toZ_(n) instead of the resistance 4 shown in FIG. 2. Further, in FIG. 3, Eshows a voltage when the conductor wire 1 operates as an antenna and thenoise current I₀ is derived. I₁, I₂ to I_(n) show the noise currentsderived by the mutual induction effect for I₀ and each of the windings 3₁, 3 ₂, - - - , 3 _(n). Therefore, from FIG. 3, following equations canbe acquired.

$\begin{matrix}\begin{matrix}\begin{matrix}{{{R_{L}I_{0}} + {j\;\omega\; M_{10}I_{1}} + {j\;\omega\; M_{20}I_{2}} + \ldots + {j\;\omega\; M_{n\; 0}I_{n}}} = E} \\{{{j\;\omega\; M_{01}I_{0}} + {Z_{1}I_{1}} + {j\;\omega\; M_{21}I_{2}} + \ldots + {j\;\omega\; M_{n\; 1}I_{n}}} = 0}\end{matrix} \\\vdots \\{{{j\;\omega\; M_{0n}I_{0}} + {j\;\omega\; M_{1n}I_{1}} + {j\;\omega\; M_{2n}I_{2}} + \ldots + {Z_{n}I_{n}}} = 0}\end{matrix} & (12)\end{matrix}$

In Expression (12) (determinant), ω is an angular frequency of the noisecurrent, M₀₁ and the like are mutual induction coefficients between theprimary-side winding (conductor wire 1) and each of the secondary-sidewindings 3 ₁, 3 ₂, - - - , 3 _(n). However, only the mutual inductioncoefficients between the primary-side winding (conductor wire 1) andeach of the secondary-side windings 3 ₁, 3 ₂, - - - , 3 _(n) are shownin FIG. 3 in order to avoid the complication in the drawing. As is wellknown, M_(mn)=M_(nm). Further, the coiled numbers N₁, N₂ and the like ofthe windings 3 ₁, 3 ₂, - - - 3 _(n) show the number of the windings 3 ₁,3 ₂, - - - , 3 _(n) and the coiled numbers thereof, and subscriptnumbers of those and subscript numbers of the current I, the inductanceL of the windings are set to coincide with each other. Further, themutual induction coefficient M_(nm) is defined as follows, where k=1.M _(nm) ±k√{square root over (L _(n) L _(m))}

By solving Expression (12) while considering the above, I₀ to I_(n) canbe acquired. Therefore, the noise failure power I₀ ²R_(L) and the noisepower consumed in each of the impedance elements Z₁ to Z_(n) of each ofthe secondary-side windings 3 ₁, 3 ₂, - - - , 3 _(n) can be found.

The inventors of the present invention measured the relation between theinductance L₀ given by the conductor wire 1 inserted into the hollowhole 2 a of the cylindrical core 2 and the inductance L_(m) given by thewindings 3 by L, C, R meters and have found that there is a followingrelation of Expression (13) between the inductance L₀ given by theconductor wire 1 inserted into the hollow hole 2 a of the low-losscylindrical core 2 and the inductance L_(m) given by the windings 3 withthe coiled number N_(m) as in the case of Expression (1) describedabove.L _(m) ≈N _(m) ² L ₀  (13)

When calculating Expression (12) by using the relation of Expression(13), it is possible to let L_(m) be equal to N_(m) ²L₀. Thus,M_(nm)=±N_(n)N_(m)L₀ can be acquired.

Further, when the impedance elements Z₁, Z₂, - - - , Z_(n) of FIG. 3 aresimply set as the pure resistances R₁, R₂, - - - , R_(n) by consideringthe consumption amount of the noise power, Z₀, Z₁, Z₂, - - - , Z_(n) ofExpression (12) become Z₀=R_(L)+jωL₀. Z₁=R₁+jωL₁=R₁+N₁ ²jωL₀, - - -Z_(n)=R_(n)+jωL_(n)=R_(n)+N_(n) ²jωL₀. Thus, the noise power consumptionamount in the resistance R_(L) and the resistances R₁, R₂, - - - , R_(n)of the secondary-side windings 3 ₁, 3 ₂, - - - , 3 _(n) can be foundfrom each of the current values I₀, I₁, I₂, - - - , I_(n) as follows.

In the case where the number of the secondary-side winding is n=1,followings can be acquired.

$\begin{matrix}{P_{RL} = {{{I_{0}}^{2}R_{L}} = {{\frac{1 + {N_{1}^{1}\left( \frac{\;{\omega\; L_{0}}}{R_{1}} \right)}^{2}}{1 + {\left( \frac{\;{\omega\; L_{0}}}{R_{1}} \right)^{2}\left( {N_{1}^{2} + \frac{R_{1}}{R_{L}}} \right)^{2}}}\frac{E^{2}}{R_{L}}} = {\alpha_{1}\frac{E^{2}}{R_{L}}}}}} & (14) \\{P_{R\; 1} = {{{I_{1}}^{2}R_{1}} = {{\frac{{N_{1}^{4}\left( \frac{\;{\omega\; L_{0}}}{R_{1}} \right)}^{2}\left( \frac{R_{1}}{R_{L}} \right)}{1 + {\left( \frac{\;{\omega\; L_{0}}}{R_{1}} \right)^{2}\left( {N_{1}^{2} + \frac{R_{1}}{R_{L}}} \right)^{2}}}\frac{E^{2}}{R_{L}}} = {\beta_{1}\frac{E^{2}}{R_{L}}}}}} & (15)\end{matrix}$

In the case where the number of the secondary-side winding is n=2,followings can be acquired.

$\begin{matrix}{P_{RL} = {{{I_{0}}^{2}R_{L}} = {{\frac{1 + {\left( \frac{\;{\omega\; L_{0}}}{R_{1}R_{2}} \right)^{2}\left( {{N_{1}^{2}R_{2}} + {N_{2}^{2}R_{1}}} \right)^{2}}}{1 + {\left( \frac{\;{\omega\; L_{0}}}{R_{1}R_{2}} \right)^{2}\left( {{N_{1}^{2}R_{2}} + {N_{2}^{2}R_{1}} + \frac{R_{1}R_{2}}{R_{L}}} \right)^{2}}}\frac{E^{2}}{R_{L}}} = {\alpha_{2}\frac{E^{2}}{R_{L}}}}}} & (16) \\{P_{R\; 1} = {{{I_{1}}^{2}R_{1}} = {{\frac{{N_{1}^{2}\left( \frac{\;{\omega\; L_{0}}}{R_{1}R_{2}} \right)}^{2}\left( \frac{R_{1}}{R_{L}} \right)R_{2}^{2}}{1 - {\left( \frac{\;{\omega\; L_{0}}}{R_{1}R_{2}} \right)^{2}\left( {{N_{1}^{2}R_{2}} + {N_{1}^{2}R_{1}} + \frac{R_{1}R_{2}}{R_{L}}} \right)^{2}}}\frac{E^{1}}{R_{L}}} = {\beta_{1}^{\prime}\frac{E^{2}}{R_{L}}}}}} & (17) \\{P_{R\; 2} - {\frac{{N_{2}^{2}\left( \frac{\;{\omega\; L_{0}}}{R_{1}R_{2}} \right)}^{2}\left( \frac{R_{2}}{R_{L}} \right)R_{2}^{2}}{1 + {\left( \frac{\;{\omega\; L_{0}}}{R_{1}R_{2}} \right)^{2}\left( {{N_{1}^{2}R_{2}} + {N_{2}^{2}R_{1}} + \frac{R_{1}R_{2}}{R_{L}}} \right)^{2}}}\frac{E^{2}}{R_{L}}} - {\beta_{2}^{\prime}\frac{E^{2}}{R_{L}}}} & (18)\end{matrix}$

In the case where the number of the secondary-side winding is n=3,followings can be acquired.

$\begin{matrix}{P_{RL} = {{{I_{0}}^{2}R_{L}} = {{\frac{1 + {\left( \frac{\;{\omega\; L_{0}}}{R_{1}R_{2}R_{3}} \right)^{2}\left( {{N_{1}^{2}R_{2}R_{3}} + {N_{2}^{2}R_{1}R_{3}} + {N_{3}^{2}R_{1}R_{2}}} \right)^{2}}}{\begin{matrix}{1 +} \\{\left( \frac{\;{\omega\; L_{0}}}{R_{1}R_{2}R_{3}} \right)^{2}\left( {{N_{1}^{2}R_{2}R_{3}} + {N_{2}^{2}R_{1}R_{3}} + {N_{3}^{2}R_{1}R_{2}} + \frac{R_{1}R_{2}R_{3}}{R_{L}}} \right)^{2}}\end{matrix}}\frac{E^{2}}{R_{L}}} = {\alpha_{3}\frac{E^{2}}{R_{L}}}}}} & (19) \\{P_{R\; 1} = {{{I_{1}}^{2}R_{1}} = {{\frac{{N_{1}^{2}\left( \frac{\;{\omega\; L_{0}}}{R_{1}R_{2}R_{3}} \right)}^{2}\left( \frac{R_{1}}{R_{L}} \right)\left( {R_{2}R_{3}} \right)^{2}}{\begin{matrix}{1 +} \\{\left( \frac{\;{\omega\; L_{0}}}{R_{1}R_{2}R_{3}} \right)^{2}\left( {{N_{1}^{2}R_{2}R_{3}} + {N_{2}^{2}R_{1}R_{3}} + {N_{3}^{2}R_{1}R_{2}} + \frac{R_{1}R_{2}R_{3}}{R_{L}}} \right)^{2}}\end{matrix}}\frac{E^{2}}{R_{L}}} = {\beta_{1}^{''}\frac{E^{2}}{R_{L}}}}}} & (20) \\{P_{R\; 2} = {{{I_{2}}^{2}R_{2}} = {{\frac{{N_{2}^{2}\left( \frac{\;{\omega\; L_{0}}}{R_{1}R_{2}R_{3}} \right)}\left( \frac{R_{2}}{R_{L}} \right)\left( {R_{1}R_{3}} \right)^{2}}{1 + {\left( \frac{\;{\omega\; L_{0}}}{R_{1}R_{2}R_{3}} \right)^{2}\left( {{N_{1}^{2}R_{2}R_{3}} + {N_{2}^{2}R_{1}R_{3}N_{3}^{2}} + \frac{R_{1}R_{2}R_{3}}{R_{L}}} \right)^{2}}}\frac{E^{2}}{R_{L}}} = {\beta_{2}^{''}\frac{E^{2}}{R_{L}}}}}} & (21) \\{P_{R\; 3} = {{{I_{3}}^{2}R_{3}} = {{\frac{{N_{3}^{2}\left( \frac{\;{\omega\; L_{0}}}{R_{1}R_{2}R_{3}} \right)}^{2}\left( \frac{R_{3}}{R_{L}} \right)\left( {R_{1}R_{2}} \right)^{2}}{\begin{matrix}{1 +} \\{\left( \frac{\;{\omega\; L_{0}}}{R_{1}R_{2}R_{3}} \right)^{2}\left( {{N_{1}^{2}R_{2}R_{3}} + {N_{2}^{2}R_{1}R_{3}} + {N_{3}^{2}R_{1}R_{2}} + \frac{R_{1}R_{2}R_{3}}{R_{L}}} \right)^{2}}\end{matrix}}\frac{E^{2}}{R_{L}}} = {\beta_{3}^{''}\frac{E^{2}}{R_{L}}}}}} & (22)\end{matrix}$

The same applies also for the case where the number of thesecondary-side winding is n=n.

In Expressions (14) to (22), E²/R_(L) shows the noise power consumed inthe equivalent noise load resistance R_(L) when the noise reduceraccording to the present invention shown in FIG. 2 is not used, and αshows the reduction degree of the noise power consumed in the resistanceR_(L) when the noise reducer is used. Further, β shows the proportion ofthe noise power consumed in each of the resistances Z₁, Z₂, - - - ,Z_(n) of the secondary-side windings 3 ₁, 3 ₂, - - - , 3 _(n) toE²/R_(L). In other words, β shows the contribution rate for the noiseenvironment purification.

Therefore, due to the existence of the noise reducer according to thepresent invention shown in FIG. 2, the noise power E²/R_(L) consumed inthe resistance R_(L) when the noise reducer is not used is reduced as isevident from Expressions (14), (16), and (19). The reduced power isconsumed in each of the resistances Z₁, Z₂, - - - , Z_(n) of thesecondary-side windings 3 ₁, 3 ₂, - - - , 3 _(n) as is evident fromExpressions (15), (17), (18), (20), (21), and (22).

Therefore, the power consumption of the noise in the noise load, i.e.,the noise reduction effect, of the noise reducer according to thepresent invention is the same as the case of the single-winding circuit.However, the noise power consumption amount by the impedance element 4connected to the winding 3 of the secondary-side winding circuit P isincreased in the case where the secondary-side winding circuit P isformed with a plurality of winding circuits P than the case where it isformed with a single-winding circuit P. The more the number of thesecondary-side winding circuits P is increased, the more the noise powerconsumption amount is increased. That is, the noise environmentpurifying function is increased.

Next, a modification example of the embodiment according to the presentinvention shown in FIG. 2 will be described. In the embodiment accordingto the present invention shown in FIG. 2, shown is a mode where theconductor wire 1 of FIG. 1 is inserted into the hollow hole 2 a of thecylindrical core 2 of a single noise reducer D. However, in a case wherea priority is given to the noise failure reduction effect for theelectronic device exposed to the electromagnetic noise interference bysacrificing the environmental electromagnetic noise reduction effect,the conductor wire 1 may be used by being inserted to the hollow hole 2a of the cylindrical core 2 of m (m=1 to n) pieces of noise reducer(s) Das shown in FIG. 4A. As the embodiment of such case, the effect of thecase where m=3 will be described.

First, the value of a shown in Expression (10) when the m-pieces areinserted comes in a form of α_(m) shown in Expression (26). Fordescribing the process of deriving Expression (26), the impedance Z ofthe winding 3 side viewed from the conductor wire 1 side inserted intothe hollow hole 2 a of the cylindrical core 2 in FIG. 1B, i.e., theimpedance of the secondary-side winding viewed from the primary side inthe transformer, is shown by Expression (23).

$\begin{matrix}{Z = {\frac{1}{1 + {N^{4}\left( \frac{\;{\omega\; L_{0}}}{R} \right)}^{2}}\left\{ {{{N^{2}\left( \frac{\;{\omega\; L_{0}}}{R_{1}} \right)}^{2}R_{1}} + {j\;\omega\; L_{0}}} \right\}}} & (23)\end{matrix}$

Thus, the input impedance Z_(in) viewed from the noise source E sidewhen m-pieces of those are placed in series can be expressed byExpression (24).

$\begin{matrix}{Z_{m} = {R_{L} + {\frac{m}{1 + {N^{4}\left( \frac{\;{\omega\; L_{0}}}{R} \right)}^{2}}\left\{ {{{N^{2}\left( \frac{\;{\omega\; L_{0}}}{R_{1}} \right)}^{2}R_{1}} + {j\;\omega\; L_{0}}} \right\}\frac{R_{L}}{1 + {N^{4}\left( \frac{\;{\omega\; L_{0}}}{R_{1}} \right)}^{2}}\left\{ {1 + {N^{4}\left( \frac{\;{\omega\; L_{0}}}{R_{1}} \right)^{2}} + {{{mN}^{2}\left( \frac{\;{\omega\; L_{0}}}{R_{1}} \right)}^{2}\left( \frac{R_{1}}{R_{L}} \right)} + {j\;{m\left( \frac{R_{1}}{R_{L}} \right)}\left( \frac{\;{\omega\; L_{0}}}{R_{1}} \right)}} \right\}}}} & (24)\end{matrix}$

Expression (25) can be acquired from Expression (24).

$\begin{matrix}{{Z_{m}} = {\frac{R_{L}}{1 + {N^{4}\left( \frac{\;{\omega\; L_{0}}}{R} \right)}^{2}}\left\lbrack {1 + {\left( \frac{\;{\omega\; L_{0}}}{R_{1}} \right)^{2}\left\{ {N^{2} + {m\left( \frac{R_{1}}{R_{L}} \right)}} \right\}^{2}}} \right\rbrack}^{1/2}} & (25)\end{matrix}$

From

${{I_{0}} = \frac{E}{Z_{m}}},$α similar to that of Expression (10) can be acquired in a form ofExpression (26) by P_(RL)=|I₀|²R_(L).

$\begin{matrix}{\alpha_{m} = \frac{1 + {N^{4}\left( \frac{\;{\omega\; L_{0}}}{R_{1}} \right)}^{2}}{1 + {\left( \frac{\;{\omega\; L_{0}}}{R_{1}} \right)^{2}\left( {N^{2} + {m\frac{R_{1}}{R_{L}}}} \right)^{2}}}} & (26) \\{\beta_{m} = \frac{{{mN}^{4}\left( \frac{\;{\omega\; L_{0}}}{R_{1}} \right)}^{2}\left( \frac{R_{1}}{R_{L}} \right)}{1 + {\left( \frac{\;{\omega\; L_{0}}}{R_{1}} \right)^{2}\left( {N^{2} + \frac{R_{1}}{R_{L}}} \right)^{2}}}} & (27)\end{matrix}$

Similarly, regarding β, provided that L₀=64 μH, N=3, the pure resistancevalue R₁ of the resistance 4 connected to the winding 3 is 1 KΩ, and m=3in Expression (26) and Expression (27), the value of α_(m) becomes −9 dBat the noise frequency of 100 kHz, −16.6 dB at the noise frequency of500 kHz, and −17.7 dB at the noise frequency of 2 MHz or more. Thus, abetter noise failure reduction effect can be achieved. However, thevalue of β_(m) showing the noise power absorption effect by R₁ becomes0.10 at the noise frequency of 100 kHz, 0.11 at the noise frequency of500 kHz, and also 0.11 at the noise frequency of 2 MHz or more.Therefore, the electromagnetic environment purifying function isdeteriorated than the case where m=1, i.e., the case of inserting singlepiece.

Further, the value of α_(m) when the pure resistance value R₁ of theresistance 4 connected to the winding 3 is set as 5 KΩ becomes −8.5 dBat the noise frequency of 100 kHz, −21.4 dB at the noise frequency of500 kHz, −28.9 dB at the noise frequency of 2 MHz, and −30.7 dB at thenoise frequency of 10 MHz or more. Thus, the noise power reductioneffect for the electronic device side is increased. However, the valueof β_(m) becomes 0.02 at the noise frequency of 100 kHz, and also 0.03at the noise frequency of 500 kHz or more. Thus, the electromagneticenvironment purifying function is deteriorated greatly to only about 3%.

As described, it is shown that even when a plurality of noise reduceraccording to the present invention are used and the conductor wires 1are inserted to the hollow holes 2 a of the cylindrical cores 2 of theplurality of noise reducers to be used, the use number m, the coilednumber N of the windings 3, the resistance value R₁ of the resistance 4connected to the winding 3 may be determined as appropriate bycalculations of the numerical values of Expression (26) and Expression(27) according to the state of the noise failure and the electromagneticenvironment where the electronic device exposed to the interference isplaced.

The interference by the electromagnetic noise occurs when the conductorwire 1 such as the earth line, the power supply line, or the likeconnected to the electronic device functions as an antenna. Thus, themode of the noise current propagated on the conductor wire 1 isbasically a common mode. However, the conductor wire 1 such as the powersupply line is of a double-line type, and it is bent at an acute angleand drawn around. Therefore, it is converted to a normal (differential)mode noise current, so that noise currents of two modes coexist in theconductor wire 1.

In a case where the double-line type conductor wire 1 such as the powersupply line is inserted and used in the noise reducer according to theembodiment of the present invention, it is considered theoretically thatthe noise failure reduction effect is exhibited only for the common-modenoise current that is the basic noise current, and that there is nonoise failure reduction effect for the normal-mode current since thenormal (differential) mode noise current flows on the two conductorwires 1 in the reverse directions from each other and cancels themagnetic flux formed within the cylindrical core 2.

Thus, in order to make the noise reducer according to the embodiment ofthe present invention effective simultaneously for the noise currents ofthe two modes, the structure shown in FIGS. 4A and 4B are proposed.However, in this case, each of the two conductor wires 1 a and 1 b ispenetrated through the hollow hole 2 a of the cylindrical core 2 of thenoise reducer D of FIG. 1 according to the embodiment of the presentinvention as shown in FIG. 4B. Therefore, the magnetic flux by a largecurrent of the power supply current and the like is generated inside thecylindrical core 2 according to the well-known “Ampere's circuitalintegral” law. However, the embodiment is a form which uses theconductor wire 1 by inserting it as described above. Thus, theembodiment corresponds to the case where the number of the primarywinding of the transformer is “1”, and it is a use form as the inductorwhere the magnetic saturation is suppressed in the best manner. Further,it is considered that the reducer that can bear a large current value ofa power supply current or the like can be achieved without having amagnetic saturation by the use of the cylindrical core 2 with a largecore diameter.

Further, in the structure shown in FIG. 4B, a plurality of noisereducers D are used to deal with the both noise currents of the normal(differential) mode. In this case, the coiled number N of the windings 3and each resistance value R₁ of the resistances 4 in each of the noisereducers D may vary from each other.

Further, as shown in FIG. 5, it is also possible to use a conventionalnoise filter technique, and parallel capacitors C may be additionallyused at input/output terminals of the conductor wires 1 a and 1 bpenetrated through the noise reducers D.

As described above, with the embodiment of the present invention, it ispossible to reduce the electromagnetic noise interference by insertingthe conductor wire such as the earth line or the power line to thecylindrical core of the noise reducer, to reduce the reflection of theelectromagnetic noise (i.e., reactive power), and to purify theelectromagnetic noise environment.

Further, since the conductor wire can be placed by being inserted intothe cylindrical core of the noise reducer, the interference caused dueto the noise currents superimposed on a plurality of earth lines andpower supply lines can be reduced effectively even when the conductorwire 1 is a single earth line or double or triple power supply lines.Furthermore, the wiring connection work of the conductor wires becomeunnecessary in many cases by using the conductor wire through insertingit into the cylindrical core of the noise reducer, so that it is highlyconvenient.

Next, a modification example of the embodiment of the present inventionwill be described. The modification example uses magnetic core materialsof different magnetic permeability values for the magnetic ring cores 2₁, 2 ₂, - - - , 2 _(n) such as the ferrite for forming the cylindricalcore 2 shown in FIG. 1, and forms the cylindrical core 2 shown in FIG. 1by stacking a plurality of magnetic ring cores 2 ₁, 2 ₂, - - - , 2 _(n)of different magnetic permeability values. The other structuresincluding the winding 3 and the impedance element 4 are the same asthose shown in FIGS. 1A and 1B.

As the cylindrical core 2 shown in FIG. 1, described is the case where aplurality of magnetic ring cores (e.g., toroidal cores) 2 ₁, 2 ₂, 2₃, - - - , 2 _(n) of equivalent magnetic permeability values arestacked. However, the cylindrical core 2 may also be formed by stackinga plurality of magnetic ring cores 2 ₁, 2 ₂, 2 ₃, - - - , 2 _(n) ofdifferent magnetic permeability values.

As the magnetic ring cores 2 ₁, 2 ₂, 2 ₃, - - - , 2 _(n) of differentmagnetic permeability values, magnetic core material such as ferrite oramorphous is used. The noise damping function of the noise reducerconstituted by staking a plurality of such magnetic ring cores 2 ₁, 2 ₂,2 ₃, - - - , 2 _(n) of different magnetic permeability values depends onthe magnetic permeability (μ=μ′−jμ″) of each of the magnetic ring cores.Each of (μ′) and (μ″) changes depending on the frequency of the current.Further, as is well known, (μ′) is a constant of proportionality of themagnetic flux formed within the magnetic ring core by the magnetic fieldthat depends on the current, and (μ″) is a constant of proportionalityof the consumption power generated within the magnetic ring core by themagnetic field. That is, the self-inductance L₀ of the magnetic ringcore is given by a following expression.

$\begin{matrix}{L_{0} = \frac{\mu\; N^{2}A}{2\pi\;\rho}} & (28)\end{matrix}$

In Expression (28), N is the number of turns coiled to the magnetic ringcore (e.g., toroidal cores 2 ₁, 2 ₂, - - - , 2 _(n)), A is the sectionalarea of the magnetic ring core (e.g., toroidal cores 2 ₁, 2 ₂, - - - , 2_(n)), and ρ is the average magnetic path length of the magnetic ringcores (e.g., toroidal cores 2 ₁, 2 ₂, - - - , 2 _(n)).

In this case, μ in Expression (28) is the real part of permeabilityvalue. Thus, precisely, μ on the left side is supposed to be written as(μ′). However, in general, it is allowed to consider (μ″) that shows themagnetic loss as 0. Therefore, it is simply expressed as (Literature:DOVER PUBLICATION, INC. Minecola, N.Y., “Roger F, Harrington”,“Electromagnetic Engineering” pp 245).

Therefore, μ regarding L₁≈N²L₀ shown in (1) of the noise reducer is(μ′), and the value thereof exhibits the frequency characteristic.

As the magnetic ring cores (e.g., toroidal cores 2 ₁, 2 ₂, - - - , 2_(n)), those having various frequencies for (μ′) and (μ″) such as Ni—Zn,Mn—Zn-based ferrite, amorphous, and the like are available on themarket. For example, there are the type which has a low (μ′) value butexhibits the inductor characteristic until the frequency characteristicof 100 MHz or more as shown in FIG. 6, and the type which has a high(μ′) value and exhibits the inductor characteristic only to thefrequency characteristic of several tens of MHz as shown in FIG. 7.

The noise reducer according to the embodiment of the present inventionis designed to achieve the object of reducing/eliminating the noisefailure by absorbing the noise power with the resistance (impedanceelement) 4 of the secondary-side winding circuit P through utilizing theinductor function of the magnetic ring cores (e.g., toroidal cores 2 ₁,2 ₂, - - - , 2 _(n)). Thus, it is desirable for the magnetic ring coremembers 2 ₁ to 2 _(n) shown in FIG. 1 to exhibit the noise reductioneffect over the wide range by mixing those having the various frequencycharacteristics described above as the (μ′) value.

Note that (μ″) is a constant of proportionality of the energy of themagnetic field derived by the current, which is consumed within themagnetic ring core member such as the ferrite, so that it does notdepend on the effect of the winding 3 of the noise reducer shown inFIG. 1. That is, it is the constant showing the noise power consumptioneffect which depends only on the material of the magnetic ring coremembers 2 ₁ to 2 _(n).

Therefore, in the noise reducer according to the embodiment of thepresent invention, it is desirable for the value of (μ″) within thelow-frequency band such as a commercial power frequency or the like tobe equal to 0, and it is desirable to employ the magnetic ring coreswhich exhibit a large value in the noise frequency band. Further, ingeneral, there are many ferrite or amorphous magnetic substances thathave such characteristic that the value in the real part (μ′) of themagnetic permeability rapidly decreases in the MHz band and value in theimaginary part (μ″) increases. However, such characteristic is the samefunction as that of the noise countermeasure product of the conventionalferrite bead shown in FIG. 12 and FIG. 13, and it can be applied to thepresent invention.

Further, another modification example of the embodiment of the presentinvention will be described. As shown in FIG. 8, this anothermodification example employs a structure in which air gaps 5 areprovided in all of (or a part of) the magnetic ring cores 2 ₁, 2₂, - - - , 2 _(n) that form the cylindrical core 2 shown in FIG. 1, andthe positions of the air gaps 5 of the magnetic ring cores 2 ₁, 2₂, - - - , 2 _(n) are relatively shifted from each other in thecircumferential direction of the ring core. The other structuresincluding the winding 3 and the impedance element 4 are the same asthose shown in FIGS. 1A and 1B.

There is a widely used technique which increases the magnetic resistancethrough providing the air gap, a narrow slot cut 5 in the magnetic ringcores 2 ₁, 2 ₂ such as ferrite or amorphous so as to increase themagnetic saturation current compared to the case without the air gap 5.In that case, it is a well-known fact that the magnetic resistance valueof the magnetic ring cores 2 ₁, 2 ₂, - - - , 2 _(n) change depending onthe width of the air gap 5 and that the effective (μ′) value isdecreased greatly compared to the case without the air gap 5.

As can be seen from Expressions (1), (10), and (11) described above, inthe noise reducer according to the embodiment of the present invention,a decrease in the (μ′) value leads to a decrease in the inductance L₀ ofthe conductor wire 1 inserted into the hollow hole 2 a of thecylindrical core 2, which results in deterioration of the noise dampingeffect.

However, existence of the air gaps 5 can ease the magnetic saturation ofthe magnetic ring cores 2 ₁, 2 ₂ by the signal (power supply or thelike) current as described above, i.e., can extend the magneticsaturation phenomenon to a greater use current value. Thus, in order toeliminate the noise current superimposed on a large current such as apower supply current, it is essential to employ the magnetic ring coreshaving the air gap 5.

However, it is extremely difficult in the noise reducer to keep thestate of a decrease in the value of the inductance L₀ of the conductorwire 1 inserted into the hollow hole 2 a of the cylindrical core 2 andthe signal current value of the power supply current, for example, to beoptimum. That is, it is not impossible but extremely difficult to setthe length of the air gap 5 as the limit with which the magnetic ringcores 2 ₁, 2 ₂, - - - , 2 _(n) are not magnetically saturated by thesignal current value and to keep the value of the inductance L₀ of theconductor wire 1 inserted into the hollow hole 2 a of the cylindricalcore 2 as the largest value as much as possible.

Thus, as shown in FIG. 8, the end faces of the neighboring magnetic ringcores 2 ₁, 2 ₂, - - - , 2 _(n) are abutted against each other and thepositions of the air gaps 5 provided in the magnetic ring cores 2 ₁, 2₂, - - - , 2 _(n) are relatively shifted from each other in thecircumferential direction of the ring cores 2 ₁, 2 ₂, - - - , 2 _(n) toarrange the positions of the air gaps 5 of the magnetic ring cores 2 ₁,2 ₂, - - - , 2 _(n) relatively shifted from each other.

As described, through arranging the positions of the air gaps 5 of themagnetic ring cores 2 ₁, 2 ₂, - - - , 2 _(n) relatively shifted fromeach other, a leakage magnetic flux in the air gap 5 of one of theneighboring magnetic ring cores is coupled again within the other one ofthe neighboring magnetic ring cores by the air gap 5 of the other one ofthe neighboring magnetic ring cores or by the end face where there is noair gap 5. Accordingly, effective magnetic permeability of the magneticring core is reduced by the air gaps 5. As a result, magnetic saturationof the magnetic ring cores 2 ₁, 2 ₂, - - - , 2 _(n) by the current flownin the winding 3 and the inductance by the winding 3 and the magneticring cores 2 ₁, 2 ₂, - - - , 2 _(n) can be set to the optimum values. Asdescribed, it is possible to suppress the magnetic saturation generatedin the cylindrical core 2 by the signal current of the power supplycurrent or the like to the minimum, and to increase the multiplicity ofuse by corresponding to a large signal current.

As an experimental example, there is described a case where theinductance value is measured when the positions of the air gap 5 of thetwo neighboring magnetic ring cores 2 ₁, 2 ₂ are shifted relatively inthe circumferential direction of the magnetic ring cores 2 ₁, 2 ₂.

As shown in FIG. 8, the winding 3 of fifty turns is coiled around thetwo magnetic ring cores 2 ₁, 2 ₂ neighboring to each other stacked intwo stages with the air gaps 5, 5, and the positions of the air gap 5 ofthe magnetic ring core 2 ₁ or 2 ₂ is shifted by θ degrees with respectto the position of the air gap 5 of the other magnetic ring core 2 ₂ or2 ₁. FIG. 9 shows the result of measuring the impedance value of suchcase measured by an impedance meter.

In FIG. 9, regarding θ (degrees) showing the positions of the two airgaps 5 and the inductance value L (L₀) given by the winding 3, the upperrow shows the shift angle θ of the air gaps 5, while the lower row showsthe inductance value L (L₀) mH given by the winding 3.

Further, there is no problem to consider the impedance Z of such case asa pure reactance, so that L (mH) as the inductance value for the changeof θ can be acquired provided that z=jX=jωL₁ and L₁=X/ω.

In the experiment, ferrite cores which have relative permeability, wereused as the ring cores 2 ₁, 2 ₂, the size of the two magnetic ring cores2 ₁, 2 ₂ was 60 mm in the external diameter, 40 mm in the insidediameter, 18 mm in thickness, and the width of the air gaps 5 was 4 mmfor the both. Further, separately from that, the inductance of a casewhere the winding 3 of fifty turns was coiled around the two magneticring cores of the same shape having no air gap 5 of 4 mm was measured bythe impedance meter. As the measured value, a fixed value of 56 mH wasacquired.

As evident from the experimental example, it is confirmed that, becausethe positional relation of the air gaps 5 of the magnetic cores 2 ₁, 2 ₂is shifted in the circumferential direction, each of the leakagemagnetic flux by the air gaps 5 is coupled again within the other one ofthe magnetic ring cores 2 ₂, 2 ₁ by the air gaps 5 of the other one ofthe magnetic ring core 2 ₁ or 2 ₂ or by the end face where there is noair gap 5. Accordingly, effective magnetic permeability of the magneticring core is reduced by the air gaps 5. As a result, it is confirmedthat there is an effect of being able to set the magnetic saturation ofthe magnetic ring cores by the current and the inductance value to theoptimum values.

While single turn of the winding 3 is shown in FIG. 1 and FIG. 8 whichshow the embodiment of the present invention, the winding 3 may becoiled for a plurality of turns.

INDUSTRIAL APPLICABILITY

The present invention is capable of reducing the noise failure in themedical equipment and computer-controlled electronic precision deviceswhile contributing to purification of the noise electromagneticenvironment.

REFERENCE NUMERALS

-   1 Conductor wire-   2 Cylindrical core-   3 Winding-   4 Resistance-   5 Air gap

The invention claimed is:
 1. A noise reducer for reducingelectromagnetic noise interference generated in an electronic device bya noise current superimposed on a conductor wire, the noise reducercomprising: a cylindrical magnetic core including the conductive wirepenetrated through a hollow hole; a winding coiled via the hollow holeof the cylindrical magnetic core; and an impedance element connected tothe winding, wherein an inductance L₀ if the conductor wire is insertedinto the hollow hole of the cylindrical magnetic core an, inductance L₁given by the winding coiled around the cylindrical magnetic core, and acoiled number N of the winding are in a relation of L₁≈N²L₀.
 2. Thenoise reducer as claimed in claim 1, wherein a plurality of magneticring cores to which the winding is provided are used as the cylindricalmagnetic core, and the conductor wire is penetrated through theplurality of magnetic ring cores.
 3. The noise reducer as claimed inclaim 1, further comprising: a plurality of secondary-side windingcircuits that are formed with the winding.
 4. The noise reducer asclaimed in claim 1, wherein magnetic ring cores of different magneticpermeability values are used as the cylindrical magnetic core.
 5. Thenoise reducer as claimed in claim 4, wherein air gaps are provided in apart of or all of the magnetic ring cores, and positions of the air gapsof the magnetic ring cores are arranged to be relatively shifted fromeach other.